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H. L. DARRAH. SERVICE OBSERVING SYSTEM. APPLICATION FIILED nov. 26, 1915.

5 SHEETS-SHEET I.

Patented Aug. 15,1916.

//1 ve n for. flak/y L. DdHd/i H L.- DARRAH. SERVICE OBSERVING SYSTEM.

V APPLICATION FILEDNOV- 26, I915. 1,194,?21. I

'5 SHEETS-SHEET 2.

Patented Aug. 15, 1916.

H. L. mum/m. SERVICE OBSERVING SYSTEM. A'PPLICATION FILED NOV. 26. 1915;

Patented; Aug. 15, 1916.

5 SHEETS-SHEET 3.

H. L. DARRAH. SERVICE OBSERVING SYSTEM. APPLICATION FILED NOV. 26, 19 15- Patented Aug. 15, 1916.

5 SHEETS-SHEET 4- ,w hy

harry A. arka/2 k l.

H. L. DARRAH. SERVICE OBSERVING SYSTEM. APPLICATION FILED NOV- 26, 1915.

Patented u 15,1916.

5 SHEETS-SHEET 5.

myth To all whom it may concern:

HARRY L. Dam an, or, CHATHAM, nnw annsnxhssrenon To wnsrnan' ELECEZEtIG COMPANY, ruconronn'rnn, on NEW YORK, N. Y., A conrons'rron or NEW "roan;

snnvron-ossnnvme SYSTEM,

master.

Specification of Letters Patent.

, rarest-easin is, rare.

Application filed November 26, 1915. Serial No. 63,480

Be it known that I, HARRY L. DARRAH, a

citizen of the United States, residing at- Chatham, in the county of Morris and State of New Jersey, have invented certain new and useful Improvements "in Service-Observing Systems, of which the following is a full, clear, concise, and exact description.

This invention relates: to serviceobserving systems for observing the character of service rendered upon, telephone lines by the operating force of telephone exchanges and more particularly to such systems in which the service upon anyone of a plurality or" telephone lines may be observed from a central point.

The object ofthis invention is to provide improved signaling means for such. a system by means of which the numbe of the telephone line, upon which the "is eing observed, may be indicated tothe ob- In accordance with this invention, there is provided a trunk circuit extending from acentral oflice to a central point, and there terminating in aservice observing desln' At the central ofiice end of the trunk circuit, there is provided apparatus by means of which any one of a plurality-of telephone lines, .to which the trunkcircuit has access and upon which a callis made, may connect the particular telephone line to the trunk circuit and cause the operation of a signaling device at the other end of the trunk circuit to furnish a signal to the observer stationed thereat, indicating that a call has been made and that the telephone has been connected to the trunk circuit. Apparatus associated with the trunk circuit, control signaling devices at the service observing desk, which operate to furnish signals to the observer to indicate when a regular operator .answers the call by plugging in on the callthe trunk circuit, which is controlled by-the telephone line upon which :1. ;:-.all has been drawings.

made and by the observer ior controlling the operation of signaling devices at the serviceobserving desk, corresponding to the telephone lines to which the trunkcircuit has access;'whereby signals are furnished the observer to indicatethe number of the telephone lineon which service is being observed.

This invention will be more fully imderstood by reference to theaccompanying drawings illustrating one embodiment A thereof.

To obtain aclear idea of the entire system, Figures 1, 2, 3, 5 and 6 of the draw ings should be arranged in the order shown in Fig. 7.

As shown in;the drawings, this invention comprises a service observing trunk D of four wires extending between central offices X and Y, At,the central oflice X,'a plurality of telephone lines terminate, two of which are shown in Fig. 1. In Fig. l is also shown an ordinary cord circuit E for interconnecting the telephone lines for conversation. In Fig. 2 there-is, shown the end ,of the service observing trunk D, which terrhinates in central oflice X. .As shown irr Fig.1 5, the end of the service observing trunk D at central oflice Y terminates in a plu- .rality of positions of a service observing desk, the portion between the dotted lines being one being anot er position G. There may be other positions, but, for convenience, only the two are shown. Associated with the service observing trunk D is apparatus for 0 indicating to the operators at the service observing desk the number of the line' upon. which service is being observed. The indi eating apparatus, which'is located on the service observing desk, is shown in Fig. 3. The service observing system embodying this invention is capable of use for obs rv ing the service upon any one of twenty-six telephone lines. ience, however, only the first and phone lines, #1 and #26, are shbwn Telephone line #1 is e p at the substation with a coin collector, while telephone line 1:26 is equipped at the central ofiice with a message register 32. Each of these lines is connected to a pair of jacks by means of cords and plugs,of four conductors. Telephone line #1 is connected to plosition F and that to the right For ccnvem jacks 139 and' 140 by means of a cord 23 and plugs 24 and 25, and telephone line #26 to jacks 141 and 142 by means of a cord 26 and plugs 27 and 28. Associated with the service observing trunk D at central ofiice X are three relays, individual to each telephone line, to which the service observin trunk D has access for connecting the trunk to the telephone line upon which a call is being made. Relays 109, 113 and 114 are individual to telephone line #1, and relays 110, 116 and 143 are individual to telephone line #26. The leads from jack 139 terminate in normally open contacts of relay 113, the lead from the upper contact of jack 140 terminates in a normally open contact of relay 114, and the lead from the lower contact of-jack 140 extends through resistance 151 and the winding of relay 101 to battery; the leads from jacks 141 and 142 are similarly associated with relays 143, 116 and 101, resistance 152 and battery. For each pair of relays 113 and 114, and 143 and 116, shown in Fig. 2, there are three leads, A, B and C. For each pair of similar relays, individual to the remaining twenty-four telephone lines not shown, there would also be leads A, B and C. The three leads A, B and C for the various twentysix pairs of relays are to be connected to the leads 1 to 7 inclusive, shown in Fig. 3, in the manner indicated in the table of Fig. 4.

At the service observing desk, there is a lamp corresponding to each'of the twentysix telephone lines to which the service observing trunk D has access. For convenience, these indicating lamps are given numbers, 301 to 326, corresponding to the number of lines, 1 to 26. Relays 144, 145, 146

and 115 and resistances 147, 148, 149, 150, 165 and 1. 6 are for the purpose of controlling the signal lamps on the service observing desk, which indicate to the operators thereat the number of the line connected to the service observing trunk D. At each operators position of the service observing desk, there is an indicating key controlling the indicating apparatus. Key 217 in position F and key 218 in position G are for this purpose. Key 206 in position F and key 214 in position G serve to connect the position apparatus with the service observing trunk D and the telephone line connected with it, while key 219 in position F and key 220 in position G are for the purposeof releasing the service observing trunk from a connected telephone line.

The subscriber of telephone line #1, initiating a call, removes the receiver from the sw'itchhook and deposits a coin 29 in the coin-box. Line relay 15 thereupon operates over a circuit from battery, through the winding of line relay 15, contact'of cut-ofl' relay 17, tip side of line, tromagn'e 30 of the coin-box and coin 29 to windings of elecground. The armature 31 of electromagnet 3.0 is unaffected by the establishment of this circuit. The operation of line relay 15 lights-line lamp 16 and causes the operation of relay 101 over a circuit from battery, through the winding of relay 101, resistance 151, lower engaging contacts of the jack 140 and plug 25, and contact of line relay 15, to

ground. Theoperation of relay 101 causes relay 102 to ground. Relay 201, in operating, causes the lighting of lamp 204 in position F and lamp 205 in position G of the. service observing desk, to indicate that a call is being made on one of the telephone lines to which the service observing trunk has access. The circuit for these lamps may be traced from battery through the contact of relay 201, the lower normally closed contacts of keys 206 and 214, and the lamps 204 and 205 in parallel to ground. The operation of relay 102 also causes the operation of relays 109 and 110 over a circuit from battery, through the windings of relays 110 and 109, upper contact of relay l02 and normal contact of relay 112 to ground. Relay 109, in operating, causesthe operation of relays 113 and 114, relay 113 operating over a circuit. from battery through the winding of relay 113, contact of relay 109, lower engaged contacts of jack 140 and plug 25, and the contact of line relay 15 to ground, and relay 114 operating over a circuit from battery through the windings of relays 115 and 114, contact of relay 109, lower engaged conthrough the winding of relay 112, upp r contact of relay 114, lower engaged contacts of jack and plug 25, and the contact of line relay 15 to ground. The operation of relay 112 causes the release of relays 109 and 110. 'Relays113 and 114, upon operating,

are locked up over portions of the circuits just traced through the windings of these two relays to the lower contact of relay 114, then through the normal contact of relay 116, winding of relay 105 and upper normal contact of relay 104 to ground. 'Relay 105 0perates,. causing the release of. relay 102,

'1ayl12, already referred to, has furnishedmeager and as long as relay 105 operated, all other telephone lines, to which this service observing trunk has access, are prevented from being connected thereto, because the eneit" 'zing circuit of relay 102 is open atithe lower normal contact of relay 105. The release of relay102 does not cause lamps 204 and 205 to be extinguished, for the operation of reground for maintaining relay 201 operated. Assuming that the lighted condition of lamp 204 is observed by the observer at position F of the service-observing desk, this observer actuates key. 206, thereby causing lamps 204 and 205 to be extinguished, and also causes lamp 207 to belighted. Signal lamp 207is responsive to the position of the connected subscribers switchhook,- as will be more fully explained later. The operation of this key 206 also connects the observers telephone 221 to the service observing trunk D. When the regular operator, upon noticing the lighted condition of line lamp 16, an-

swers by inserting the answering plug of the cord circuit E into the jack associated with telephone line #1, cutofl' relay 17 and relay 117 operate over a circuit from 'battery through lamp 18, resistance 19, sleeve of the answering plug and jack to point 20, where it branches, one branch going through the winding of cut-01f relay 17 and the other through the middle contact of relay 114:, and the windings of relays 117 and 118, to ground. Relay 118 is marginal and does not now operate. The operation of the cutoil relay releases line relay 15, extinguishing line lamp 16, and releases relay 112. The

operation of relay 117 causes relays 119 and "120 to operate in parallel over a circuit from battery through the contact of relay 117,

normal contact of relay 121, upper normal I contact of relay 119, windings of relays 119 and 120 in parallel, and upper normal contact of relay 104: to ground. The operation of relay'120 extends .the tip and ring con- 'ductors of the service observing trunk, to which are connected the limbs of telephone 'line qfitl, through to position F of the service ground.

observing desk.- The operation of relay 117 also causes the operation of relay 122 over a ,-,eircuit from battery, through the contact of relay 117 and the winding of'relay122, to

The operation of relay 122 causes the operation of relay 208 over a circuit from coil 209, ring conductor of the service observing trunk, retard coil 124, middle normalfcontact of relay 108, and middle contact of relay 122 toground. Relay 20 8, in operating causes the lighting of lamp 210, which vindicates-to the observer that the regular operator has answered the call. The cir-.

cuit of lamp 210 is from battery, through the contact ofrelay 208, contact 211 of key 206 and lamp 210to ground. The operation of relay 122' also connects battery through its lower contact to a voltmeter relay 126, shown within the dotted lines in Fig.- 3., and completes Wheatstone bridge circuit in which resistance 127 forms the first arm, resistance 128 the second arm, resistance 21 third and fourth arms. The bridge in this condition is unbalanced, causing coil 131 to move to close contact 132, which short-cir-- cuits condenser 133 and resistance 13%, whereupon relay 135 operates over a circuit from battery through resistance 136, contact 132 of the voltmeter relay 126 and the winding of relay 135 to ground. The operation of relay 135 furnishes ground for relay 201 in place of the ground which was removed therefrom by the release-of relay 112, whereby lamp 207 remains lighted to, indicate to the observer that the subscriber has-the receiver ofi the switchhook. When the subscriber restores the receiver to the switclihook, supervisory relay 22 releases, removing resistance 21 from parallel relation to lamp 18, thereby changing the resistance of the third arm of the bridge to such an extent that the bridge becomes balanced.

,The coil 131 then assumes its normal posiation of relay 105-, hereinbeforereferred to,

would cause the operation of relays 121 and 212 over a circuit from battery, through the winding of relay 212, contact 213 of key 214, contact 215 ofkey206, lower normal contact of relayy216, winding of relay 121,

lower normal contact of relay 119, wind ing of relay 128, normal contact-there of and alternate contact of relay 105 to ground. Relay. 128 is marginal-and does not now operate. The establishment of this circuit has the following, important functions, as will more fully appearlaterz. (1)

,makes it possible for the service oloservii'ig trunk to be released automatically by a regular operator when pluggingin to answer, provided the observer has not taken up the call provides ag lard signal to Warn the observer in case the position appa;- ratus at the service observing desk has been 7 disconnected from the trunk circuit wlthout releasing the trunk circuit, and (3) furnishes a guard signal to the observer in case the subscriber takes the receiver ofi the switchhook, thus connecting and locking the telephone line to the service observing trunk, and then restores the receiver to the switchhook before the regular operator answers by plugging in. This guard signal notifies the observer that the trunk circuit should be released.

Relay 212 in operating, causes lamp 239 in position'F and lamp 210 in position G to be lighted. Lamps 204 and 205 are also lighted, due to the operated condition of relays 112 and 201. The lighted condition of lamps 20 1 and 239 and lamps 205 and 240 in positions F and G respectively, notifies the observers that the telephone line, on

which a call has been made, has been locked onto the service observing trunk.. If the key 206 at the service observing desk is actuated before the regular operator plugs in to answer, relays 121 and 212 will be released'so that upon the subsequent plugging in by -the regular operator, lamp 210 will be lightedto apprise the observer of this fact. If the regular operator plugs in to answer before the observer takes up the call (by actuating key 206), the operated condition of relay 121 permits the service observing trunk to be released, and relay 117 will operate, causing the operation of relay 101 over a circuit from battery through the contact of relay" 117, alternate contact of relay 121 and upper winding of relay 104 to ground. Relay 104 in operating, releases relays 105, 113, 114.- and 115, thereby disconnecting the service observing trunk from telephone line #1 upon which a call was made. All apparatus associated with the service observing trunk thereupon returns to normal condltion, ready to connect the service observing trunk to another of the telephone lines to which the trunk has access when a call [is made.

Function #1 of the circuit through relays 121 and 212 is thereby accomplished With reference to function #2 above re ferred, to, if the observer, after completing an observation on telephone line #1, disconnects the position apparatus by restoring key 206 to normal position without releasing thetrunk circuit by actuating release key 219,.lamps 239 and 240 will be lighted to warn the observer that the trunk circuit a has not been released.

As tofunction #3 of the'circuit, including relays 121 and 212, the making of a call on telephone'line #1 causes the lighting of lamps 20 1 and 205 and locks the telephone line to the service observing trunk (as here: inbefore explained), but if the subscriber on telephone line #1 restores the receiver to i the sw tchhook before the regular operator fillSlVQ'i-b by plugging in and before the observer takes up thecall, relay 112 will release, causing tluflaznps 204C and 205 to be extinguished. Lamps 239 and- 240 will remain lighted to notify the observers that the service observing trunk should be released.

Upon connection being completed between thecalling telephone line #1 and the called telephone line, the regular operator by actu- V ating coin collect key 33 causesthe coin 29 to be deposited in a proper receptacle. This is accomplished in this manner,--actuation of key 33 causes the nergization of electromagnet 30 over a circuit from negative battery 34, through winding of relay 36, upper alternate contact of key 33, tip contacts of the plug and jack, winding of electromagnet 30 and coin 29 to ground. Upon the energization of electromagnet 30, armature 31 is moved about its pivot point to close its ,lower contact and in so doing causes the deposit of the coin 29 into a suitable receptacle in any well-known manner. The closure of the lower contact locks up the electromagnet 30 as long as key 33 remains actuated. The closure of the circuit from negative battery 34 operates relay 36 to cause the lighting of pilot signal 37. Negative battery 34 and positive battery 38 are of higher voltage than the common battery at the central office, being preferably of 110 volts, While the voltage of the ordinary central oflice battery is 7 preferably 24. The actuation of key 33 also causes the operation of relay 155 overacircuit from negative battery 34: through the winding of relay 36, upper alternate contact 3 of key 33, tip contacts of the plug and jack, upper engaged contacts of the plug 24 and jack 139, upper contacts of relays 113, 120 and 122, winding of relay 155 and normal contact thereof to ground. The operation of relay 155 removes the short circuit fromabout polarized relays 156 and 153, whereupon polarized relay 153 operates. ized relay 153 operates on negative-battery from 34, but does not operate on positive battery from 38, while polarized relay 156 operates on positive battery from 38 but does not operate on negative battery from 34:.

. Relay 155 in operating also causes the oper- Polartraverses the prim'arywinding of repeating coil 222, whereupon current will be induced n the secondary thereof. The path of the induced flow of current in thesecondary of repeating coil 222 includes the receiver of the" 157 to release, whereupon the tone to theobseryer ceases.- In a similar manner, the

, observer, receives a tonewhen the regular operator refunds a coin, as in the case where the calling subscriber does not obtain connection with a definite line called for. Coin refund key 41-is operated when-the regular operator refunds the coin, whereupon relay 40 operates to light the pilot signal 37. The electr'omagnet 30 'being energized, moves armature 31 about its pivot point to close. its upper contact, and in so, doing refunds the coin to this subscriber in any well-known manner. Relay 155 also operates, permit ting polarized relay156 to operate and cause ing the operation of relay 157. Interrupter 161, instead of 158, will thereupon be in- -cluded in circuit with battery and primary of repeating coil 159. The number of segments on interrupters 158 and 161 being different, the observer receives tones of different frequencies, and is thereby enabled to,

determine by these different tones when the re ular operator collects or refunds a coin.

in order for the observer to identify the telephone line upon which service is being observed, the indicating lamps shown in 6 are provided and mounted upon the Fig. service observing desk. The observer at some time while a telephone line, is connected to the service observing trunk will actuate a key which controls the niain indicating circuit. Assuming'now that the observer at position F actuates key 217, signal lamp 223 will be lighted to assure this observer that she has control of the indicating circuit. It will be noted that battery is fed through series contacts of keys. 217 and 218 in positions F, G, and through similarkeys in other positions, if there be any providedat the service observing desk, so that only one observer can have control of the indicating circuit at a time. Actuation of ra 217 also causes the opera: tion of relay 224 and causes the intermittent operation and release of electromagnet 328, the operating circuittherefor being from a source of alternating current 327 through the primary of a transformer 329, the winding. of electromagnet 328, the contact thereof and the right-hand alternate contact of key 217 to ground. Electromagnet 328, in operating, removes the short-circuit from about resistance 330, whereupon electromagnet releases its armature, causing the the short-circuit to be established again. This cycle of operating and releasing continues as long as key 317 remains actuated. The operation of relay 224: causes the opera tion of relay 216 over a circuit from battery through the contact of relay 22 1:, contact 225 of key 206 and the winding of relay 216 to ground. Relay 216, in operating, causes the operation of relay 202 over a circuit from battery, through the contact of relay 22 1, contact 225 of key 206-, the winding of relay 202 and the upper alternate contact-of relay 216 to ground. Relay 216, in operating, also causes the operation or relay 162 over a circuit which includes the secondary of repeating coil. 331, middle and lower alternate contacts of relay 216 and the windings of relay 162. The current in this path is current'induced from the primary of repeating coil 331,- which is in circuit with the secondary of transformer 329 into which has been induced a high-frequency-alternating current from the varying flow of alternating current through the primary of transformer 329. Relay 162 operates, open ing its contact,- permitting the release of relay 160. Relay 160, in releasing, closes its alternate contact, completing a circuit for'relay 108, which operates. Relay 108, in operating, causes the operation of relays 332 and 333 over a circuit from battery, through resistance 150, contact of relay 115, middle alternate contact of relay 108, retard coil 124:, ring conductor of the service observing trunk D, retard coil 209, lower alternate contact of relay 202, windings of relays 332 and 333, lower alternate contact of relay 216, winding of relay 121, lower normal contact of relay 119-, winding of relay, 128, upper normal contact thereof and alternate contact of relay 105' to ground. Relay 332, in operating, causes the operation of relays 334;, 335 and 336 over a circuit from battery through the windingsof these three relays and the alternate contact of relay 332, to ground. The operation of relay 334 completes a circuit for lamp 301 from battery, through lamp 301, upper alternate contact of relay 334, upper normal contacts ofrelays 337 and 338, and normal contacts of relays 339 and 340 to ground. The lighting of this lamp indicates to the service observer that the line upon which service is being observedis No. 1 of the twenty-six to which the service observing trunk has access. It is to be here noted that the actual numbers of the twenty-six lines, to which the service observing trunk has access at any one time, have been associated with the numbers 1 to 26,

and that the service observers have lists sociated with the actual number of the line Lac upon which service is being observed. The

. release of key 217, afterindicating lamp 301 and the observer has determined the numher of the telephone line under observation, it is necessary to release the telephone line from the service observing trunk. To do this, the observer operates release key 219,

which connects a high voltage battery 226, preferably of 110 volts, through the contact of key 219, contact 227 of key 206, lower normal contact of relay 216, winding of relay 121, lower normal contact of relay 119, winding of relay 128, normal contact thereof and alternate contact of relay 105 to ground. Relay 128 will thereupon be operated, completing a circuit for relay 104 from battery, through the lower alternate contact of relay 128 and the upper winding of relay 104 to ground. The operation of relay 104 causes relays 105', 113, 114 and 115 to release, whereupon telephone line No. 1

will be disconnected from the service observing trunk D.

Keys 206 and 214 at the service observing desk are preferablyof the locking type,

for either key must remain actuated while a line connected with the trunk is under observation, and when actuated both the upper and lower movable contacts are moved to disengage the normal contacts and to engage the alternate contacts.v Keys 217, 218, 219 and 220 at the service observing desk are preferably of a non-locking type, for these remain actuated for only a short time. Y

Suppose that a call be made on telephone line No. 26; the operation of line relay 42, in addition to lighting the line lamp, causes the operation of relay 101, which, in turn willcause the operation of relay 102. Re lay 102 inoperating, causes the operation of relays 109 and 11'0, and the operation of the latter relay completes a circuit from relays 143 and 116, the circuit ofthe former being from battery, through the Winding of relay 145, Winding of relay 143, contact of relay 110, lower engaged contacts of the jack 142 and plug 28, and the contact of line relay 42 to ground, and the circuit of relay 116 being from battery, through winding of relay 146, the winding of relay 116 contact of relay 110, engaged contacts of the jack 142 and the plug 28, and the contact of relay 104 to ground. The. operation of relay 102 also causes the operation of relay 201 which causes the lighting of lamps 204 and 205 in positions F and G of the service observing desk. The operation of relay 105 causes the release of relay 102,

Which, in turn, releases relays 109 and 110. The release of relay 102 also removes the ground which controls the lighting of lamps 204 and 205, but the lamps remain lighted, for relay 112 operates immediately after the operation of relay 116 and furnishes a ground in place of that removed by the release of relay 102. Assuming .that the-observer at position G has noticed the lighted condition of lamp 205, sheactuates key 214, causing lamps 204 and 205 to be extinguished and lamp 228 to be lighted. The

observers telephone 229 will also be connected to tip and ring conductors of the service observing trunk. The regular operator, noticing the lighted condition of the line lamp, now answers in the usual manner by inserting the answering plug into the jack associated with telephone HIIGNQ'QG, whereupon the cut-off relay 43 and relay 117 will be operated. Relay 118 does not I lay 117 causes the operation of relays'119, 120 and 122. The operation of relay '122 operate at this time. The operation of re-.'

connects battery to the voltmeter relay 126.

Since telephone line No. 26 is a message register line, the fourth arm of the Wheatstone bridge of the voltmeter relay will be" made up of the winding of the cut-ofif relay and the winding of the electromagnet of message register 32 in parallel, the windings of relays 117 and 118 in series and:

resistance 130 connected in parallel. It is to be noted that this fourth arm of the bridge, in the case of a telephone line equipped with a message register, contains the winding of the electromagnet of the message register, whereas in the case of a line not equipped with a message register, this Winding is replaced by resistance'129,

When the subscriber on telephone line No. 26 has been connected with a called telephone line, the regular operator registers the call on message register 32 by the actuation of key This is accomplished by establishin the following circuit upon the actuation fo key 35 from battery 44, preferably of 36 volts, through the winding of the electromagnet of a position register 45, contact 46 of key 35, sleeve contacts of answering plug and jack, both windings ofelectromagnet 32, of the. line register to ground- The electromagnets of; both the line 'register 32. and" position register 45 are energized, attracting.

their armatures to cause the registration of the call. When the armature of electromagnet 32 is attracted, the righthandwinding thereof is short-circuited, whereupon this magnet will remain energized from the regular central oflice battery after the release of key 35. Vhen the electromagnet of the position register 45 and the electromagnet 32 of the line register were energized; relay 118 was operated over a circuit from battery- 44 through the winding of the electromagnct of position register 45, contact 46 of key 35, sleeve contacts of the answering plug and jack, upper engaged contacts of the plug 28 and jack 142, middle contact of relay 116, and windings of relays 117 and 118 to ground. Relay 118 is responsive to a flow of current from a 36 volt battery, but is not responsive to flow of current from the regular central oilice battery of 24 volts. Re-' lay 118 in operating, causes the operation of relay 230 over a circuit from battery through the winding of relay 230, middle IIOI'lllfllCOlltilCt of relay 216, retard coil 231, lower normal contact of relay 108 and contact of relay 118 to ground. Relay 230 in operating, lights lamp 232 and operates buzzer 233, the circuit therefor being from battery through the contact of relay 230, contact 234 of key 214, lamp and buzzer 233 and contact thereof in parallel to ground. The lighting of the lamp and the operatien of the buzzer indicate to the observer that the regular operator has registered a call on the telephone line which'i's connected to the service observing trunk. The release of key 33 by the regular operator releases relays 118 and 230, whereupon lamp 232 is extinguished and buzzer 233 ceases tooperate. The voltmeter relay 126 operates in the same manner as hereinbefore described in connectionwi t-h a call on telephone line No. 1 to control the signal lamp 235 instead of 207 for indicating the position of the subscrib- Signal ers switchho ok to theobserver. v lamp 235 was operated when the regular operator plugged in to answer the call on telephone line #26 ,to indicate this fact to the.

observer. The signal lamp 236 and buzzer 237 are for the pprpose of indicating to the operator in position F when the regular operator registers on a line, that is, should the observer in position F be observing the service on a line with which is associated a line register. To'get an indication of the number of the line upon which service is being observed, operator G actuates key 218, which causes the operation ofrelays 238, 202, 216, 162, the release of the relay 160 and the operation of relay 108. The operation of these relays causes the operation of relays 339, 340, 341, 342 and 333. The energizing circuit for relays 339 and 340 is from battery through resistance 165,- lower contact of re lay 143, lower alternate contact of relay 108, a

retard coil 231, middle alternate contact of relay 216, windings ofrelays 340 and 339, lower alternate contact of relay 216, winding of relay 121, lower normal contact of re.- lay 119, winding of relay 128', normal contact thereof and alternate contact of relay 105 to-ground. The circuit for relays 341 and 342 is from battery through. resistance 148, contact of relay 145,,upper alternate contactof relay 108,, retard boil 106, tip con ductor of the service observing trunk, retard coil 203, upper alternate contact of re:

lay 202, windings of relays 341 and 342,--

lower alternate contact of relay 216, winding of relay 121, lower normal contact of-re lay 119, winding of relay 128, normalcontact thereof and alternate contact of relay 105 to ground. Relay 333 operates over a.

circuit from battery through resistances 150 and 149, contact of relay 146, middle alterring conductor of the service observing trunk, retard coil 209, lower alternate contact' of relay 202, windings of relays 332 and .333, lower alternate contact of relay 216, winding of relay 121, lower normal contact of relay 119, winding of relay 128,

normal contact thereof and alternate contact Indicating lamp 326 is now 345, lower normal contact of relay 336, lower 7 alternate contact of relay 338 and alternate contact of relay 340 to ground. server at position G receives an indication, by means of the lighted condition of 326, of the number of the-line upon service is being observed. .Release of'the indicating gontrolling circuit key 218 permits all apparatus associated with the indicating circuit to assume its normal condition. The telephone line #26,upon which serviceis being observed, may be released by the actuation of release key 220 by the observer at position G, the apparatus-tune tioning in precisely the same manner as described in connection with the release of telephone line #1.

It is to be noted that relays 339 and 340 are always in series, the. same being true of relays 341 and 342, and relays 332 and 333. Relays 339, 342 and 333 always operate when a circuit is completed through their windings. Relays 340, 341 and 332 are marginal and do not operate when either-resistances 147 and 148, or-149 and 150, or 165 and 166 85; nate contact of relay 108, retard coil 124, .1

being preferably of about 15,000 ohms, while resistances 148, 150 and 165 are low, each being preferably of about 200 ohms. The manner of connecting resistances 147, 148, 149, 150, 165 and 166 in circuit with relays 339, 340, 341, 242, 332, and 333 depends enit will be evident that the manner of con .tirely upon the manner in which the leads A, B and C, for the two relays individual to a telephone line, are connected to the leads 1 to 7 inclusive. From the table in Fig. 4,

necting these leads is different for. each line. It will be clear, therefore, Without further description, that upon the actuation of either key 219 or 220 in positions F or G of the service observing desk, the proper indicating lamp will be lighted to indicate to the observer the number of the telephone line upon which service is being observed.

What is claimed is:

1. In a service observing system, a trunk circuit extending from a central ofiice to a service observing desk, a plurality oftelephone lines terminating at the central ofiice, means associated With the trunk circuit for automatically connecting a calling telephone line with the trunk'circuit, a signaling device 'at the service observing desk for each of the telephone lines, apparatus comprising marginal relays adapted to cooperate to cause the operation of the signaling device corresponding to the telephone line connected to the trunk circuit to indicate the number of the connected telephone line, and means controlled by the observer for causing said apparatus to cooperate.

2. In a service observing system, a trunk circuit extending from a central ofiice to a service observing desk,'a plurality of telephone lines terminating at the central oflice, a plurality of resistances at the central oifice, means associated with the trunk circuit for connecting a calling telephone line with the trunk circuit and for selecting one or, more of the resistances, a source of current, a signaling devi e at the service observing desk for each f the telephone lines, apparatus comprising marginal adapted .to cooperate to cause the operation of the signaling device corresponding to the telephone line connepted to the trunk cirrelays cuit to indicate the number of theconnected telephone line, a key at the service observing desk, and a relay operatingupon the actuation of the key to include the source of current, the selected resistance or resistances and said apparatus in circuit to cause the cooperation of said apparatus.

3. In a service observing system, a trunk ratus comprising threesets of relays, one of each set being marginal, adapted to cooperate to cause the operation of the signaling device corresponding to the telephone line connected to the trunk circuit to indicate the nhmber of the connected telephone line, a key at the service observing desk, and a 'relay operating upon the actuation of the key to include the source of current, the selected resistance or resistances and one or more sets of said relays in circuit to cause the cooperation thereof i 4. In a service observing system, a trunk circuit extending from avcentral ofiice to a service observing desk, a plurality of telephone lines terminating at the central office, a plurality of high and low resistances, means associated with the trunk circuit for connecting a calling telephone line With the trunk circuit and for selecting one or more of the resistances, a source of current, a signaling device atthe service'observing desk for each of the telephone lines, a plurality of relays adapted to cooperate to cause'the operation of the signaling device corresponding to the telephone line connected to the trunk circuit to indicate the number of the connected telephone line, and a relay op erating under control of the observer to cause the operative association of the source of current, the. selected resistance or resistances and said relays, whereby the signaling device corresponding to the connected telephone line is. operated.

In witness whereof, I hereunto subscribe my name this 24th .day of November, A. D. 1915.

HARRY L. DARRAH. 

